The ability of microorganisms to survive in the presence of antibiotics. Chance mutations have provided some bacteria with genes for enzymes that destroy antibiotics such as penicillins, cephalosporins, or aminoglycosides. Other mutations have changed the structure of bacterial cell walls formerly penetrable by antibiotics or have created new enzymes for cellular functions previously blocked by drugs.
See: vancomycin-resistant enterococci; resistance transfer factor; methicillin-resistant Staphylococcus aureus

The indiscriminate use of antibiotics provides the selection pressure that creates ever more resistant strains. The most effective, and frequently ignored, measure to reduce the spread of many organisms is scrupulous hand hygiene after contact with patients.